Ground-protection means for electric locomotives



L. J. HIBBARD 2,722,572

GROUND-PROTECTION MEANS FOR ELECTRIC LOCOMOTIVES Nov. 1, 1955 FiledSept. 11 1951 To Aux-Motor Contractors INVENTOR Lloyd J. Hibbord. BY

ATTURNRY 2,722,572 it atented Nov. 1, 1955 GROUND-PROTECTION MEANS FORELECTRIC LOCOMOTIVES Lloyd J. Hibbard, Pittsburgh, Pa., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application September 11, 1951, Serial No. 246,063

Claims. (Cl. 191-8) My invention relates to the protection ofelectrically propelled locomotives or other vehicles, and it hasparticular relation to that type of vehicle, including practically alltrolley-powered electric locomotives, in which space-limitations forbidthe carrying of circuit breakers which are adequate to interruptshort-circuit currents in the vehicle. It has thus been the practice,for many years, to protect such vehicles, in case of short-circuits, bygrounding the pantograph or other current-collecting means, thus forcingthe substation breakers to remove power from the trolley-wire, afterwhich, when it has been made certain that the power is off, thepantograph is lowered away from contact with the trolley-wire. Care mustbe taken not to lower the pantograph while a shortcircuit current isflowing, as both the wire and the pantograph are certain to be seriouslydamaged by the resulting arc, and the wire may be melted in two, andbrought down on the locomotive or on the right-of-way.

In such cases, it is universally the custom to use a power-operatedpantograph-lowering means, which is driven from compressed air, or othervehicle-carried source of auxiliary-purpose power, which might also be abattery which needs to be charged, or a prime-moverdriven generatorwhich needs to be brought up to operating speed. The same source ofauxiliary-purpose power is also used for actuating thepantograph-grounding switch.

A short circuit on an electric locomotive is caused by a failure of theground-insulation of the equipment, and most such short-circuitconditions result from the accidental presence of two grounds, at twocircuit-portions having a difference of potential therebetween. In orderto detect such an accidental ground, it is necessary to place anintentional grounding-connection on some portion of the circuit, and toprovide a suitable groundfault-protective relay which will respond tothe faultcurrents which then flow in the intentionalgrounding-connection upon the occurrence of an accidental ground at someother point. A protective relay of this kind is the so-calledpantograph-relay which is described in Patent No. 2,106,844, grantedFebruary 1, 1938, on an application fiied in 1934, by Harder, Taliaferroand myself.

Locomotives of the above-described type are dangerously vulnerableduring the or minutes, more or loss, which are required for pumping upair on a dead locomotive. It has happened, several times, that there hasbeen an accidental ground-fault on such a locomotive, and that theconsequential fault-currents have caused transformer-fires, and otherdamage, before the poweractuated pantograph-grounding switch could beactuated and the pantograph lowered.

It is an object of my invention, therefore, to provide aground-protection equipment in which the intentional ground issubstantially removed until air-pressure is available.

My invention also relates, more specifically, to the ground-protectionof a rectifier-powered locomotive or vehicle, in which single-phasepower is received, on the vehicle, and is transformed, by means ofrectifiers, into direct-current power, which is fed to one or moredirectcurrent traction-motors, as described and claimed in my copendingapplication Serial No. 120,331, filed October 8, 1949, patented April28, 1953, number 2,636,995. In such a vehicle, it is necessary ordesirable to provide two ground-protective means, one being thealternating-current ground-protective relaying equipment, such as hasjust been mentioned, for the protection of the step-downpower-transformers which are used on such vehicles, and the otherground-protective means being a direct-current ground-protectiveequipment, which may, in general prinv ciple, be similar to theground-detection signaling systems which have heretofore been used towarn the engineman of the presence of an accidental ground in thedirect-current traction-motor circuits of diesel-electric locornotives.In my rectifier-powered locomotive, I prefer to use an intentionaldirect-current grounding-circuit, on some part of the motor-circuitwhich is at different directcurrent potential than the midpoint of thetransformer secondary, while the traction-motors are operating, and touse alternating-current ground-protective means when the traction-motorsare not operating.

The direct-current ground-detecting relay, which was previously used, ondiesel-electric locomotives, merely to provide a signal-indication, isnow used as a means for deenergizing the direct-current traction-motorcircuits in the event of an accidental ground-fault either in themotor-circuits, or in the rectifiers, or in the secondary winding of thepower-transformer. At the same time, the intentional direct-currentgrounding-circuit is opened and the intentional alternating-currentgrounding-circuit is closed, so that, if any particular ground-fault isnot cleared by the deenergization of the direct-current circuits, thematter of ground-fault protection must be taken over by the pantographrelay, or alternating-current ground-fault protective means, ultimatelyresulting, if

necessary, in a grounding of the pantograph, followed,f when thesubstation breakers have opened, by an auto-.

matic lowering of the pantograph.

Modern power-rectifier systems commonly use singlephase ignitrons, whichare rectifying devices of a type having suitable ignition-circuit meansfor making each rectifier-device conductive at the beginning of eachconducting period. In such rectifying systems, when it is desired todeenergize the direct-current output-circuit of the rectifiers, it hasbeen known, and is generally recognized as being desirable, toincapacitate the ignition-circuit means, as well as, or even in lieu of,opening a circuit-breaker or breakers in the direct-currentoutput-circuit. In a rectifier-powered locomotive, in which themotor-load is deenergized by incapacitating the ignition-v circuit meansof the rectifiers in response to a groundcurrent flowing through theoperating coil of a directcurrent ground-detecting relay, thedirect-current load is disconnected very quicklyin about one-quarter ofa cycle of the alternating-current supply-line. This time is muchsmaller than the time necessary to open a directcurrent circuit-breakeror 1ine-switch, and it is too short a time to build up an adequate fluxin a holding-coil, such as has previously been used on the ground-faultdetectors on diesel-electric locomotives.

A feature of my present invention is, therefore, to energize theholding-coil of the direct-current ground-protecting relay with a steadycurrent which is only slightly below the pick-up value, or approximatelyat the holding-in value, during the normal fault-free operation of thetraction-motors, and to increase this holding-coil current to a safe orstrong holding-in value, when said ground-protection relay is energized,thus permitting the holdingcoil to build up its flux to the valuenecessary for holding the relay in or in its actuated condition, withinthe quarter-cycle time which is available for this purpose. In this way,I avoid the violent pumping (alternate opening and closing) of thedirect-current protective relay and the direct-current circuit-breakersor line-switches.

With the foregoing and other objects in view, my invention consists inthe circuits, systems, combinations, apparatus, parts, and methods ofdesign and operation, hereinafter described and claimed, and illustratedin the accompanying drawing, the single figure of which is adiagrammatic view of much simplified circuits and apparatus illustratingthe essential features of my present invention, and such other parts asnecessarily cooperate therewith, and omitting all signalling-circuitsand the many other refinements, and safeguards, and duplicates, andniceties of control and operation, such as are necessary in any modernlocomotive, but which are not essential to an understanding of mypresent improvements.

The illustrated equipment includes a trolley-wire 13, which is energizedfrom a substation which is represented by a single-phase generator Gwhich is connected to the trolley-line 13 through an overloadcircuit-breaker 14. All the rest of the equipment which is shown on thedrawing is a very great simplification of the equipment which is carriedby one locomotive, which may be considered to be schematically indicatedby means of a retractable pantograph 15, which may be raised or loweredinto or out of engagement with the trolley-wire 13, so that itconstitutes a retractable current-collecting means for moving along thetrolley-wire 13, as the locomotive moves. The trolleywire 13 isrepresentative of any external alternating-current power-supply line forthe locomotive. The pantograph 15 is connected, on the locomotive, tothe highvoltage lead 16 for the primary winding 17 of a stepdownpower-transformer, which is also provided with a multitapped secondarywinding 19. The primary winding 17 has a low-voltage lead 20 which isgrounded at 21.

The secondary winding 19 has a midpoint tap X, on one side of which area plurality of voltage-changing taps T1, T2 and T3, of successivelyincreasing voltages, and on the other side of the midtap X, there arecorresponding voltage-changing taps T1, T2 and T3. These secondary tapsare used, in connection with tap-switches or contactors C1 to C12, andpreventive coils 22 and 23, to provide a variable voltage for theanode-leads 25 and 26 of two ignitrons 1A and 1B, which may be regardedas being representative of any suitable kind of power-rectifiers of atype having ignitor or ignition-circuits I-1A and I-1B for making eachrectifier conductive at the beginning of each conductive period. Thecathode-circuits of the two rectifiers are connected together, in acommon circuit 992 which constitutes the positive terminal of thedirect-current output-circuit of the rectifiers. While I have describedthe rectifier-connections in their usual polarity, it will beunderstood, of course, that the polarities might have been reversed, sothat the anode-leads 25 and 26 would then become cathode-leads, whilethe common cathode-terminal 992 would then become a commonanode-terminal. The other terminal of the direct-current output-circuitof the rectifiers is the midpoint tap-connection of the secondarywinding 19.

The directcurrent output-terminals 992 and X are used to energize one ormore direct-current traction-motors, which are represented by anarmature A, a serially-connected interpole-winding 27, and a main-fieldwinding 28, the latter being connected in series with the armature Athrough a reverser 29. The motor-circuit also commonly includes aripple-reducing choke-coil 30.

It is necessary to use some sort of motor-controlling switching-meansfor controlling the motor-operation and the motor-speed. In the drawing,this controlling-means is represented by two anode-breakers orline-switches L1 and L2, the twelve tap-switches C1 to C12, and a mastercontroller MC, the whole system being very much simplified to itssimplest possible form which is deemed adequate for illustrating theprinciples of my present invention. The master controller MC controlsthe operation 4 of the tap-switches C1 to C12 through suitableinterlocks 31, which are intended to be a schematic representation orsuggestion of the intricate interlocking-system which is moreparticularly described and claimed in my copending application SerialNo. 232,811, filed June 21, 1951, now Patent No. 2,691,748.

My present invention relates to an improved means for protecting such alocomotive, or other types of electrically propelled locomotives,against short-circuits such as are usually caused by accidental grounds.As previously intimated, there is never allocated any room, on suchlocomotives, for an overload circuit-breaker which is heavy enough tointerrupt a fault-current in the locomotive. Such fault-currents ascannot be cleared in any other way, are cleared from the locomotive bymounting, on the roof, a pantograph-grounding switch GS, having acontact 33 which connects the high-voltage pantograph-lead 16 to thegrounded low-voltage lead 20 through a circuit 33. The grounding-switchGS is an electrically controlled, pneumatically operated switch, as arealso some of the other heavy-duty switches or contactors, such as thetapswitches C1 to C12 and the line-switches L1 and L2. For the purposeof more clearly illustrating my invention, this pantograph-groundingswitch GS is shown, on the draw ing, as being a pneumatically operatedswitch, comprising an electrically controlled valve V1 for admittingcompressed air tr. a cylinder 34 for closing the switch-contact 33. Thevalve V1 is provided with a magnet-coil, which may be identified by thesame letters, GS, which identify the switch itself.

The GS ground-switch valve V1 receives compressed air through piping 35which is connected to a compressedair tank 37, which is carried by thelocomotive, and which is normally kept pumped up by means of a pump orcompressor P which is driven by a suitably controlled compressor-motorM.

This compressed-air tank 37 may be regarded as being symbolic of anysuitable locomotive-carried source of auxiliary-purpose power, foractuating any desired auxiliary or non-traction equipment on thelocomotive. It is to be understood, of course, that, so far as mypresent invention is concerned, I am not limited to the kind ofvehicle-carried auxiliary-purpose power which is provided, but only bythe fact that there is some kind of auxiliary-purpose power which issometimes in need of replenishment, particularly when an engineman firstenters a dead locomotive and starts to put it into operating-conditionafter a considerable period of idleness. The source of auxiliary-purposepower might also be exemplified, for example, by the locomotive-battery,which is represented on the accompanying drawing by means of itspositive and negative terminals (l) and and which is used for energizingthe various relaycoils or contactor-controlling coils or magnet-valvecoils, as this battery is an auxiliary-power source which may needcharging or replenishing when a dead locomotive is first energized.

Means must also be provided for at times automatically retracting orlowering the pantograph 15 so that it will be out of contact with thetrolley-wire 13; and this is done, in the illustrated apparatus, bymeans of a pantograph-down valve V2, which admits compressed air to apiston-cylinder 38 which lowers the pantograph 15 against the tension ofits raising-spring 39. The pantograph-lowering valve V2 is opened bymeans of a valvemagnet coil 40.

In order to detect faults or accidental grounds in a locomotive, it isusually necessary to provide an intentional grounding-circuit at someselected point in the secondary-winding circuit. In my rectifier-poweredlocomotive, I prefer to use two intentional grounding circuits, only oneof which-is used at a time.

When the traction-motor circuit is not energized, it is desirable to usethe kind of grounding-circuit which is commonly used in alltrolley-powered alternating-current locomotives. This is analternating-current grounding-circuit which is connected at someselected intermediate potential-level on the secondary winding 19,preferably near the midtap point X. In the drawing, this intentionalalternating-current grounding-circuit is shown between the secondarytaps X and T1, being provided by means of an autotransformer 41 having amidtap 979, which is connected to a circuit 124, through the makecontact42 of a changeover ground-circuit relay GAC. The conductor 124 isconnected through a grounding circuit 43 to a ground 44, usually througha grounding resistor 45 which is normally shunted by a ground-cutoutswitch 46. This intentional alternating-current grounding-circuit97942-i24434644 reduces the voltage-strains to ground, on thetransformer-secondary 19, and upon such auxiliary motor-equipment as isenergized from secondary taps near the midpoint X, but if thisgrounding-circuit were left on, during the tractionmotor operation, itwould force the rectifier cathodecircuit 992 and the motor-fields 27 and28 to the full direct-current voltage above ground, thus imposingvoltage-strains on the ground-insulation of these parts.

When the traction-motor is operating, i prefer to open the intentionalalternating-current grounding-circuit and to substitute an intentionaldirect-current grounding-circuit which is connected to some selectedpart of the direct-current traction-motor circuit, preferably a parthaving a direct-current potential which is substantially different fromthe midpoint of the secondary winding when the traction-motor A is inoperation. This directcurrent grounding-point may be at someintermediate direct-current potential or, when there is only onetraction-motor per pair of rectifiers, as shown, the rectifiercathode-circuit 992 may be intentionally grounded, through a groundingresistor 56, which is in turn connected, through a circuit 984, to theoperating coil GDC of a direct-current ground-fault detector which isdesignated by the same letters, GDC. From the coil GDC, thedirect-current groundingcircuit continues, through a conductor 983, to amake-contact 51 of an auxiliary relay H, and thence, through a conductor982, to a backcontact 52 of the ground-circuit changeover switch GAC,and thence to the ground 53. The operating coil GDC of thedirect-current ground-circuit detector is thus responsive to theground-fault currents which will flow in the intentional direct-currentgrounding-circuit 992-- 984-983-982-53 whenever there occurs anaccidental ground at any other point in the secondary-winding circuit ofthe main power-transformer 1'719. This direct-current groundingcircuitplaces the rectifier cathodes and the traction-motor fields at groundpotential, thus reducing the ground-insulation strains on these parts,but it raises the potential on the ground-insulation of thetransformer-secondary 19 and on the auxiliary motorequipment which isenergized from near the midpoint X of the transformer.

As an alternating-curent protective-relay means, I pre fer to use thepantograph-relay which has been used successfully for many years, oneform of which is shown in the previously mentioned Harder et al. patent.This relay is shown to the left of the transformer-primary 17, and it isdesignated by the usual letters PR. It is driven by a shaded-polesingle-phase motor 54 having two socalled overload-coils 55 and 56 andtwo so-called differential coils 57. The two overload-coils 55 and 56are connected in series, with their intermediate connectingpointconnected to the previously-mentioned conductor 124, the outer terminalsof the coils 55 and 56 being connected to conductors 115 and 116,respectively. The two diiferential coils 57 are connected between theconductor 124 and a conductor 114, this connection including thesecondary of a current transformer 58, the primary of which is connectedin the intentional alternating-current grounding-circuit 43. Theconductors 115 and 116 are connected to the respective inner terminalsof two current transformers 60 and 61 which are located respectively inthe grounded low-potential lead 20 and in the high-voltagepantograph-lead 16 of the primary winding 17. The outer terminals of thecurrent transformers 60 and 61 are connected to the conductor 114.

The pantograph relay PR thus responds to the various types ofalternating-current faults which may occur on the main power-transformer1719. An overcurrentcondition energizes the overload-coils and 56, andthus causes a response of the pantograph relay PR. If an accidentalground should occur in the primary circuit 17 of the power-transformer,an unbalanced current-flow will occur in the two current transformersand 61, thus energizing the differential coils 57, and again causing aresponse of the pantograph relay PR. On the other hand, if an accidentalsecondary-circuit ground should occur at any point other than theintentional alternatingcurrent grounding-circuit 4197942-4344, theresulting ground-current will flow through the current transformer 53,again energizing the differential coils 57, and again causing a responseof the pantograph relay PR.

The PR motor 54 drives the moving parts of the pantograph-relay PRthrough a suitable reduction-gear, and these moving parts arediagrammatically represented in the drawing in a developed view, whichrepresents the moving element of the pantogroph-relay PR as movingvertically, against the bias of gravity, although, in actual practice,the moving parts will be on a rotating disc, as shown in the Harder etal. patent. The reduction-gearing for the PR motor 54 is shown,therefore, as a rackand pinion gearing 62 which lifts the moving partsof the relay. First, there is a latch-dog 63 which engages a pivotedlatch-arm 64 so as to normally hold the moving parts of the PR relay ata point which is about a third of the way up from the lowermost positionto the topmost position of which the moving parts are capable. Thelatch-arm 64 is normally held in its latching position, against a stop65, by means of a holding-coil 66, against the bias of a spring 67 whichtends to move the latch-arm 64 out of engagement with the latch-dog 63,whenever said dog is raised out of the notch at the end of thelatch-arm.

The PR holding-coil 66 is normally energized whenever the maintransformer is energized, as by being energized from the secondary-tapsX and T1. When my locomotive is provided with a direct-currentgroundingcircuit 992-6=lb984(GDC coil)98351-982 52-53, it is desirableto interpose an insulating transformer between the PR holding-coil 66and the secondary leads X and T1, as indicated at 68, so as to relievethis hold-coil from any extra ground-insulation strains when thedirect-current grounding-circuit is in use.

The PR latch-arm 64 carries a normally open contact 69, which is usuallycalled the D contact of the pantograph-relay PR. This contact is openwhen the latcharm 64 is engaged by the dog 63, or when the hold-coil 66is energized.

Below the latch-dog 63, the moving element of the pantograph-relay PR isshown as being provided with a tripping dog 70 which engages a roller71, as the PR relay continues to move after disengaging the latch-dog 63from the latch-arm 64. The roller 71 is carried by a pivoted contactarm72, and moves this arm past .the dead center of its biasing spring 73,so as to trip said contact-arm and open its normally closed contacts 74and 75, which are commonly known as the A contacts of thepantograph-relay PR. This contact-arm 72 can be reset to its normalclosed position, by means of a reset-coil 76.

Below the tripping-dog 70, the moving member of the PR relay is shown ashaving a final contact-making means, which is diagrammaticallyrepresented as the mov-. ing contact-member 77 of the so-caled B contactwhich is closed when the PR relay reaches the furthest limit of itsactuated movement, which ocurs after the A contact-arm 72 has beentripped.

'If the PR latch-holding coil 66 should become deenergized after thelatch-dog 63 has been disengaged from the latch-arm 64, the PR motorcoils 55, 56 and 57 being simultaneously deenergized, the moving elementof the PR relay will return (drop, in the illustrated diagram) back pastits illustrated normal latched position and will keep on going until itcloses a so-called C contact which is shown at the extreme lower end ofthe moving element of the PR relay.

Whenever the pantograph-relay PR trips its A contact arm 72, its openedcontact 74 deenergizes all of the tap-switches C1 and C12 by opening thecircuit between the positive battery-terminal (-1-) and a conductor 500which is connected to the positive supply-line 501 of the tap-switchcoils C1 to C12, through an L2-in interlock 80, which is closed when theline-switch L2 is closed.

The conductor is also connected to the valvemagnet coil H of anauxiliary, pneumatically operated relay which is designated by the sameletter, H, so that the deenergization of the conductor 5% by the PR Acontact 74 will deenergize this relay H. The relay H has a valve V3which is energized from a compressedair line 81 through a shut-off valveV4 which is connected to the main air-line 35, but which keepsair-pressure out of the line 81 until the pressure in the main air-line35, and in the air-tank 37, has reached a certain minimum value which issumcient to operate the ground-switch valve V1 and thepantograph-lowering valve V2. It will be understood that this auxiliaryrelay H thus acts as a pressure-responsive relay, which is not energizedwhen an adequate air-pressure supply is not available on the locomotive,and this same relay is also deenergized whenever the PR A contact 74 istripped open.

When the auxiliary relay H is in its deenergized position, asillusrated, it does several things. Starting at the top of the movingelement of the H-relay, as shown in the drawing, this relay is providedwith two makecontacts 82 which are open when the relay is deenergized,thus disconnecting the excitation-apparatus 33 of the rectifiers 1A and18 from the transformer-taps X and T1 from which it is normallyenergized.

Next, on the H-relay, is a back-contact 84 which, in the deenergizedposition of the relay, connects a conductor 48 to one of the terminals560 of the PR reset-coil 76 so as to make it possible for this resetcoil to be energized when the engineman returns his master controller MCto the off position, and then depresses a reset-pushbutton 85, thuscompleting the reset-circuit from the conductor 48 through thereset-button 85, a conductor 192, and the master controller MC.

Continuing the description of the H-relay contacts, we come to a contact86, which is open when the H-relay is deenergized, thereby opening acircuit between two conductors 445 and 446, making it impossible toinitially energize the operating-coil GAC of the grounding-circuittransfer-relay GAC. This H-relay contact 86 is by-passed by aholding-circuit 87 on the GAC switch, so that the dropping out of theH-relay will not deenergize the GAC switch if it was already energized.

The next contact of the H-relay is the previously mentioned make-contact51, which, when the H-relay is deenergized, opens the direct-currentground-circuit between the points 992 and 53.

At the bottom of the H-relay contact-carrying element, there is amake-contact 88 which, if the master controller MC is on any of itson-positions, when the H-relay becomes deenergized, will deenergize acircuit 387, which will in turn deenergize the operating coil PC of afiringcircuit relay PC, as well as the operating coils L1 and L2 of thetwo line-switches L1 and L2. Thus, from the negative terminal at themaster controller MC, a circuit can be traced through the conductor 36,a back-contact 89 on the direct-current ground-detector relay GDC, aconductor 383, the H-relay contact 88, the conductor 387, and theoperating coil FC, to the positive terminal When the firing-circuitrelay PC is deenergized, it closes a backcontact 91, which shortcircuits the excitationapparatus 83, making it impossible for eitherrectifier tube 1A or IE to fire again thereafter. When the firingcircuitrelay PC is energized, it closes a make-contact 92, which closes acircuit between the conductor 387 and a conductor 229 which energizesthe two line-switch operating-coils L1 and L2.

When these line-switches L1 and L2 are energized, they close theirrespective main-circuit contacts 95 and 96 in the anode-circuits and 26,respectively. The lineswitch L2, when it is closed, also closes itspreviously mentioned make-contact 80, or L2-in interlock in the positivesupply-circuit 501 of the tap-switches C1 to C12, and it also opens aback-contact 97, or L2-out interlock, in series with the conductor 445in the energizing-circuit of the ground-circuit changeover-switch GAC.

Coming back to the tripping of the pantograph-relay "A contact 74, itwill be noted that the deenergization of the circuit 500 alsodeenergizcs a branch-circuit 557 which is used to deenergize otherauxiliary-motor contactors, as indicated by legend in the drawing,thereby deenergizing blower-motors and other equipments (not shown)which normally receive their energization from the transformer-secondary19.

The purpose of the PRA contacts 74 and 75 is to deenergize all equipmentwhich is normally connected to the transformer, so that, if the faultwhich is detached by the PR relay is in that equipment, rather thanbeing in the transformer itself, such a fault will be cleared by thetripping of the A contact-arm 72, thereby permitting the PR relayinstantly to return to its original normal position, which is shown inthe drawing, and per: mitting the engineman to reset the tripped Acontactarm 72, by means of his pushbutton 85, after he has made theproper investigation to ascertain the cause of the fault.

The other PR A contact 75, which is open when the A contact-arm 72 istripped, deenergizes a terminal 112 of an inverted magnet-coil C of aninverted pneumatic compressor-controlling relay or contactor having thesame letter-designation C. This compressor-controlling contactor C has avalve V5 which is spring-biased, at 98, toward an open position, whereinair is fed from the air-line 81 to a piston-chamber 99. The C-contactorvalve V5 is closed whenever the magnet-coil C is energized. Theenergizing'circuit for this magnet-coil C includes the conductor 112,the A contact 75, and also a conductor 32 and a contact 101) of agovernor Gov. which is energized from the air-line so as to deenergizethe magnet-coil C, and thus admit air to the C-relay pistonchamber 99,whenever the air-pressure reaches its desired value which is to bemaintained in the air-tank 37. When the piston-chamber 99 of thecompressor-controlling relay C is energized with compressed air, itopens its two contacts 101 and disconnects the compressor-motor M fromits supply-lines which are the transformer-taps T1 and T1, respectively.

If the fault which caused the pantograph-relay PR to trip its A contacts74 and 75 is cleared by the tripping of said contacts, the engineman,after ascertaining and removing the cause of the fault, can reset the Acontact-arm 72 by means of his reset-pushbutton 85, as above described.

If, however, the fault is in either one of the transformer windings 17or 19, the fault-current will continue to flow after the PR Acontact-arm 72 has been tripped, and the pantograph-relay PR willcontinue its movement to the very end, at which time it will close its Bcontact 77, thus energizing a circuit 24 which will energize theground-switch magnet-coil GS, thereby causing the pantographgrounding-switch GS to ground the pantograph 15 at its switch-contact33. This short-circuits the external power-source which is representedby the trolleywire 13, and the fault-current continues to flow throughthe current-transformer in the grounded conductor 20,

9 thereby keeping the pantograph-relay PR energized, and holding its Bcontact 77 closed, until the trolley-wire 13 has been deenergized by theopening of the substation breaker 14.

When the substation breaker 14 opens, the pantographrelay PR nowreceives no energy at all, neither in its motor 54, nor in its latch-armholding-coil 66, so that the latch-arm 64 is springopened, and thepantographrelay PR returns all the way to its lowermost position, atwhich point it closes its C contact, and energizes a circuit 167 whichenergizes the magnet-coil 40 of the pantograph-lowering valve V2. Inthis manner, it is made certain that all power is off of thetrolley-wire 13 before the pantograph is lowered, thereby avoiding thedanger of drawing a destructive arc when the pantograph is lowered. Whenthe pantograph 15 is once lowered, it is latched down, as by means of alatch 102. After this occurs, the situation demands the personalattention of the engineman, and the duty of the automatic equipmentceases.

When power again comes back on the trolley-wire 13, while thepantograph-relay PR is in its lowermost position, and while itslatch-arm 64 is spring-biased to its contact-closing position, whereinit closes its D contact 69, the PR motor 54 is again energized, in acircuit extending from the motor-conductor 114 through the D contact 69,a conductor 978, and the secondary of an auxiliary transformer 103, andthence back to the circuit 124 of the pantograph-motor 54. The auxiliarytransformer 103 is energized from the secondary conductors X and T1 ofthe main power-transformer 17-19, so that it will receive power wheneverthe pantograph 15 is again raised into contact with a live trolley-wire13. The D contact 69 of the PR relay is designed so that it will remainclosed until the PR latch-dog 63 returns to a position above thelatch-arm 64, at which time the latch-holding coil 66 will be permittedto return the arm to its normal latching position, the relayresetting Dcontact 69 will deenergize the PR relay, and the latch-dog 63 willreseat itself in the forked end of the latch-arm 64.

The "direct-current ground-detector relay GDC has a hold-coil 104, whichis energized, across the batteryterminals and through a conductor 447, aresistor 105, a conductor 451, and all of the on-positions of the mastercontroller MC. The value of the resistor 105 is such that the currentthrough the hold-coil 104 is approximately at, or just below theholding-in value at which this coil alone would be able to hold thedirectcurrent ground-protector relay GDC in its actuated position, onceit has been actuated, even after its main operating-coil GDC has beendeenergized. As shown, the two coils GDC and 104 are on separatemagnetic circuits, each with its own armature which is represented by asmall circle within the circle which represents the coil, these twoarmatures being both connected to the movable contact-carrying elementof the relay. It will be understood, however, that both coils could beon the same magnetic circuit.

It Will be recalled, and is evident from the drawing, that thedirect-current grounding-circuit connection is completed, between thecathode-circuit 992 and the ground 53, upon a closure of both themake-contact 51 of the auxiliary relay H and the back-contact 52 of theground-circuit change-over switch GAC. The makecontact 51 is closedwhenever the auxiliary relay H is energized, that is, whenever there isan adequate airpressure effective on the low-pressure shut-off valve V4,While at the same time the PR A contact 74 is closed. The direct-currentground-circuit contact 52 is closed whenever the ground-transfer relayGAC is deenergized.

To initially energize the ground-transfer relay GAC requires anoff-position of the line-switch L2, closing its out-interlock 97, aswell as an energized position of the auxiliary relay H, closing itsmake-contact 86. However,

once this GAC relay is energized, its holding-circuit 8 7 keeps saidrelay energized, regardless of the condition of the H-relay, until theline-switch L2 is energized, which occurs at the time when thetraction-motor A is being energized or operated. When this occurs, theL2-out interlock 97 deenergizes the ground-transfer relay GAC, causingit to open its alternating-current grounding-connection 42, and to closeits direct-current grounding-contact 52, thus opening thealternating-current grounding circuit from 979 to 44, and closing thedirect-current grounding-circuit from 992 to 53.

If, while the traction-motor A is in operation, and while thecathode-circuit 992 is intentionally grounded as just described, anaccidental ground should occur at any other point in thesecondary-winding circuit of the main powertransformer 17-19, aground-circuit fault-current will flow through the intentionaldirect-current groundingcircuit which contains the operating coil GDC ofthe direct-current ground-detector GDC, thus actuating said detector andopening its back-contact 89, which instantly deenergizes both thefiring-circuit relay FC and the two line-switches or anode-breakers L1and L2. This holds true, notwithstanding the fact that themaster-controller lead 36 is energized, for energizing these elements,since the traction-motor A is operating and the master controller MC isthen on one of its on-positions 1 to 9.

The deenergization of the line-switches L1 and L2 would deenergize thetraction-motor A, but these lineswitches are heavy contactors, which arenot as quick, in their operation, as the firing-circuit relay PC which,when deenergized, closes its back-contact 91, which short circuits (orotherwise incapacitates) the ignition-energy supply-means 83 for theigniter-circuits I-1A and I18 of the tWo rectifiers 1A and 1B, thuspreventing each of said rectifiers from refiring again at the beginningof another half-cycle of the alternating-current supply-line 13. Thefiring-circuit relay FC thus deenergizes the directcurrenttraction-motor A very quickly, say in something like one quarter of thesupply-line cycle, after an actuation of the direct-currentground-detector GDC and the consequent deenergization of saidfiring-circuit relay PC.

As soon as this direct-current ground-detector relay GDC is actuated, itcloses a make'contact 106 which by-passes the resistor and increases thecurrent through the holding-coil 104 to a value at which it will safelyhold the relay in its actuated position, even when its mainoperating-coil GDC is deenergized by the interruption of the currentthrough the rectifiers 1A and 113. Since it is much easier to slightlyincrease the magnitude of the magnetic flux in the hold-coil 104, thanto build it up from zero to an effective relay-holding value, I thusmake sure that the direct-current ground-fault relay GDC does not dropout again as soon as the cathode-circuit 992 is deenergized.

While I have shown alternative grounding-circuits, under the selectivecontrol of a changeover-switch GAC, it is to be understood that eitherthe alternating-current grounding-circuit 979 to 44, or thedirect-current grounding-circuit 992 to 53 could be omitted. It may benoted that the alternatingeurrent grounding-point 979 is at one end ofthe direct-current traction-motor circuit, while the direct-currentgrounding-point 992 is a part of the secondary circuit, and if thisdirect-current groundingpoint 992 is grounded when the rectifiers aredeenergized, it will hold the secondary midtap X at ground-potentialthrough the direct-current traction-motor circuit between X and 992.

While I have shown and described my invention in a single illustrativeform of embodiment, and in an extremely simplified form of embodiment,which is intended to clearly indicate the essential principles of myinvention, without confusing details, I wish it to be understood that anactual locomotive-installation will be very much more complicated,involving the duplication or multiplication of parts, and the additionof many ancillary features and details which contribute to the safe andsatisfactory performance of the locomotive or otherelectrically-propelled vehicle. I also wish it to be understood that myinvention is not altogether limited to a rectifier-powered locomotive,or to a trolley-powered locomotive. In short, I wish it to be understoodthat the essential spirit of my invention will not be avoided by manyobvious changes, such as the omission or addition of parts, or thesubstitution of equivalents. I desire, therefore, that the appendedclaims shall be given the broadest construction consistent with theirlanguage.

I claim as my invention:

1. An electrically propelled vehicle having tractionmotor means, aretractable current-collecting means for moving along an externalalternating-current powersupply line, motor-energizing means including atrans former having a primary winding energized from saidcurrent-collecting means, and a secondary winding for supplying powerfor said traction-motor means, poweractuated retraction-means for attimes retracting said current-collecting means out of contact with itsexternal power-supply line, a vehicle-carried source of auxiliarypurposepower for actuating said retraction-means, means for providing anintentional grounding-circuit at some selected point in thesecondary-winding circuit, a collectorshort-circuiting means for attimes providing a shortcircuiting circuit across said power-supply line,said shortcircuiting circuit including said retractablecurrent-collecting means, and a protective-relay-means responsive tofault-currents in the intentional grounding-circuit due to an accidentalground at some other point, said protective-relay-means including meansfor causing an actuation of said collector-short-circuiting means, andfurther including means for then, in response to a cessation ofsubstantial current-flow in said short-circuiting circuit, causing anenergization of said retraction-means to actuate the same; said vehiclebeing characterized by having also, in combination with the items justmentioned, an auxiliary control means having an actuating-means which isresponsive to the condition of operativeness of said vehicle-carriedsource of auxiliary-purpose power, said auxiliary control-means alsohaving controlled-contactmeans adapted to cause the initial completionof said intentional grounding-circuit only at a time when saidvehicle-carried source of auxiliary-purpose power is in a satisfactoryoperating-condition.

2. The invention as defined in claim 1, characterized by theprotective-relay-means including means for first preventing theenergization of the traction-motor means,

and means for then, if a fault-current still continues,

causing the actuation of said collector-short-circuiting means.

3. A rectifier-powered vehicle having direct-current traction-motormeans, a rectifier-assembly comprising at least two single-phaserectifying devices, a retractable current'collecting means for movingalong an external alternating-current power-supply line, a transformerhaving a primary winding energized from said currentcollecting means,and a secondary winding for supplying power from opposite sides of itsmid-point and feeding said power to said two rectifying devices,respectively, at rectifying-device terminals of one polarity,circuitmeans for connecting the other terminals of said two rectifyingdevices to constitute one terminal of the directcurrent traction-motorcircuit, said secondary winding having a mid-point connection whichconstitutes the other terminal of the direct-current traction-motorcircuit, power-actuated retraction-means for at times retracting saidcurrent-collecting means out of contact with its external power-supplyline, a vehicle-carried source of auxiliary-purpose power for actuatingsaid retractionrneans, means for providing an intentionalgroundingcircuit at some selected part of the direct-currenttractionmotor circuit, said part having a direct-current potential whichis substantially different from the mid-point of the secondary windingwhen the traction-motor means is in operation, and a protective-relaymeans responsive to fault-currents in the intentional grounding-circuitdue to an accidental ground at some other point, saidprotective-relay-means including means for causing a deenergization ofsaid traction-motor circuit, and an auxiliary control means having anactuating-means which is responsive to the condition of operativeness ofsaid vehicle-carried source of auxiliary-purpose power, said auxiliarycontrol-means also having controlled-contactmeans adapted to remove saidintentional grounding circuit when said vehicle-carried source ofauxiliarypurpose power is not in a satisfactory operating-condition.

4. A rectifier-powered vehicle having direct-current traction-motormeans, a rectifier-assembly comprising at least two single-phaserectifying devices, supply-means for providing single-phase power on thevehicle, a transformer having a primary winding energized from saidsupplymeans, and a secondary winding for supplying power from oppositesides of its mid-point and feeding said power to said two rectifyingdevices, respectively, at rectifyingdevice terminals of one polarity,circuit-means for connecting the other terminals of said two rectifyingdevices to constitute one terminal of the direct-current tractionmotorcircuit, said secondary winding having a mid-point connection whichconstitutes the other terminal of the direct-current traction-motorcircuit, motor-controlling switching-means for controlling themotor-operating energization of each of said rectifying devices fromsaid secondary winding, said motor-controlling switching-means having anactuating-means, means for at times providing an intentionalalternating-current grounding-circuit at some selected intermediatepotential-level on the secondary winding, and ground-circuitswitching-means having an actuating-means which is responsive to thecondition of said motor-controlling switching-means in respect tomotor-operation or non-operation, said ground-circuit switching-meansalso having contacts for preventing the completion of thealternating-current grounding-circuit when the traction-motor means isin operation, and for completing the alternating-currentgrounding-circuit when the traction-motor means is not in operation.

5. A rectifier-powered vehicle having direct-current traction-motormeans, a rectifier-assembly comprising at least two single-phaserectifying devices, supply-means for providing single-phase power on thevehicle, a transformer having a primary winding energized from saidsupplymeans, and a secondary winding for supplying power from oppositesides of its mid-point and feeding said power to said two rectifyingdevices, respectively, at rectifyingdevice terminals of one polarity,circuit-means for connecting the other terminals of said two rectifyingdevices to constitute one terminal of the direct-current tractionmotorcircuit, said secondary winding having a mid-point connection whichconstitutes the other terminal of the direct-current traction-motorcircuit, motor-controlling switching-means for controlling themotor-operating energization of each of said rectifying devices fromsaid secondary winding, said motor-controlling switching-means having anactuating-means, means for at times providing an intentionaldirect-current grounding-circuit at some selected part of thedirect-current traction-motor circuit, said part having a direct-currentpotential which is substantially different from the mid-point of thesecondary winding when the traction-motor means is in operation, meansfor at times providing an intentional alternatingcurrentgrounding-circuit at some selected intermediate potential-level on thesecondary winding, and changeover switching-means having anactuating-means which is responsive to the condition of saidmotor-controlling switching-means in respect to motor-operation ornon-operation, said changeover switching-means also having contacts forcompleting the direct-current grounding-circuit and preventing thecompletion of the alternating-current grounding-circuit when thetraction-motor means is in operation,

13 and for completing the alternating-current groundingcircuit andpreventing the completion of the directcurrent grounding-circuit whenthe traction-motor means is not in operation.

6. A rectifier-powered vehicle having direct-current traction-motormeans, a rectifier-assembly comprising at least two single-phaserectifying devices, a retractable current-collecting means for movingalong an external alternating-current power-supply line, a transformerhaving a primary winding energized from said currentcollecting means,and a secondary winding for supplying power from opposite sides of itsmid-point and feeding said power to said two rectifying devices,respectively, at rectifying-device terminals of one polarity,circuit-means for connecting the other terminals of said two rectifyingdevices to constitute one terminal of the direct-current traction-motorcircuit, said secondary winding having a mid-point connection whichconstitutes the other terminal of the direct-current traction-motorcircuit, poweractuated retraction-means for at times retracting saidcurrent-collecting means out of contact with its external power-supplyline, a vehicle-carried source of auxiliarypurpose power for actuatingsaid retraction-means, motor-controlling switching-means for controllingthe motor-operating energization of each of said rectifying devices fromsaid secondary winding, means for at times providing an intentionalalternating-current groundingcircuit at some selected intermediatepotential-level on the secondary winding, switching-means having anactuating-means which is responsive to the condition of saidmotor-controlling switching-means in respect to motoroperation ornon-operation, said switching-means also having contacts for preventingthe completion of the alternating-current grounding-circuit when thetractionmotor means is in operation, and for completing thealternating-current grounding-circuit when the tractionmotor means isnot in operation, a collector-short-circuiting means for at timesproviding a short-circuiting circuit across said power-supply line, saidshort-circuiting circuit including said retractable current-collectingmeans, an alternating-current protective-relay-means responsive tofault-currents in said alternating-current groundingcircuit due to anaccidental alternating-current ground at some other point, saidalternating-current protectiverelay-means including means for causing anactuation of said collector-short-circuiting means, and furtherincluding means for then, in response to a cessation of substantialcurrent-flow in said short-circuiting circuit, causing an energizationof said retraction-means to actuate the same, and an auxiliary controlmeans having an actuating-means which is responsive to the condition ofoperativeness of said vehicle-carried source of auxiliarypurpose power,said auxiliary control-means also having controlled-contact-meansadapted to cause the initial completion of said intentionalalternating-current grounding circuit only at a time when saidvehicle-carried source of auxiliary-purpose power is in a satisfactoryoperatingcondition.

7. The invention as defined in claim 6, characterized by saidalternating-current protective-relay-means including means for firstpreventing the energization of the traction-motor means, and means forthen, if a faultcurrent still continues, causing the actuation of saidcollector-short-circuiting means.

8. A rectifier-powered vehicle having direct-current traction-motormeans, a rectifier-assembly comprising at least two single-phaserectifying devices, a retractable current-collecting means for movingalong an external alternating-current power-supply line, a transformerhaving a primary winding energized from said currentcollecting means,and a secondary winding for supplying power from opposite sides of itsmid-point and feeding said power to said two rectifying devices,respectively, at rectifying-device terminals of one polarity,circuit-means for connecting the other terminals of said two rectifyingdevices to constitute one terminal of the direct-current tranction-motorcircuit, said secondary winding having a mid-point connection whichconstitutes the other terminal of the direct-current traction-motorcircuit, poweractuated retraction-means for at times retracting saidcurrent-c0llecting means out of contact with its external power-supplyline, a vehicle-carried source of auxiliarypurpose power for actuatingsaid retraction-means, motorcontrolling switching-means for controllingthe motoroperating energization of each of said rectifying devices fromsaid secondary winding, means for at times providing an intentionaldirect-current grounding-circuit at some selected part of thedirect-current traction-motor circuit, said part having a direct-currentpotential which is substantially different from the mid-point of thesecondary winding when the traction-motor means is in operation, meansfor at times providing an intentional alternatingcurrentgrounding-circuit at some selected intermediate potential-level on thesecondary winding, changeover switching-means having an actuating-meanswhich is responsive to the condition of said motor-controllingswitching-means in respect to motor-operation or nonoperation, saidchangeover switching-means also having contacts for completing thedirect-current grounding-circuit and preventing the completion of thealternatingcurrent grounding-circuit when the traction-motor means is inoperation, and for completing the alternating-current grounding-circuitand preventing the completion of the direct-current grounding-circuitwhen the tractionmotor means is not in operation, a direct-currentprotective-relay-means responsive to fault-currents in thedirect-current grounding-circuit, said direct-currentprotective-relay-means including means for putting the motorcontrollingswitching-means in a condition for discontinuing the motor-operation, acollector-short-circuiting means for at times providing ashort-circuiting circuit across said power-supply line, saidshort-circuiting circuit including said retractable current-collectingmeans, an alternating-current protective-relay-means responsive tofault-currents in the alternating-current grounding-circuit due to anaccidental alternating-current ground at some other point, saidalternating-current protectiverelay-means including means for causing anactuation of said collector-short-circuiting means, and furtherincluding means for then, in response to a cessation of substantialcurrent-flow in said short-circuiting circuit, causing an energizationof said retraction-means to actuate the same, and an auxiliary controlmeans having an actuating-means which is responsive to the condition ofoperativeness of said vehicle-carried source of auxiliarypurpose power,said auxiliary control-means also having controlled-contact-meansadapted to cause the initial completion of said intentionalalternating-current grounding-circuit only at a time when saidvehicle-carried source of auxiliary-purpose power is in a satisfactoryoperatingcondition, said controlled-contact-means being further adaptedto remove said intentional direct-current grounding-circuit when saidvehicle-carried source of auxiliarypurpose power is not in asatisfactory operating-condition.

9. The invention as defined in claim 8, characterized by saidalternating-current protective-relay-means including means for firstpreventing the energization of the traction-motor means, and means forthen, if a faultcurrent still continues, causing the actuation of saidcollector-short-circuiting means.

10. A rectifier-powered vehicle having direct-current traction-motormeans, a rectifier-assembly comprising at least two single-phaserectifying devices of a type having ignition-circuit means for makingeach rectifying device conductive at the beginning of each conductingperiod, supply-means for providing single-phase power on the vehicle, atransformer having a primary winding energized from said supply-means,and a secondary winding for supplying power from opposite sides of itsmid-point and feeding said power to said two rectifying devices,

respectively, at rectifying-device terminals of one polarity,circuit-means for connecting the other terminals of said two rectifyingdevices to constitute one terminal of the direct-current traction-motorcircuit, said secondary winding having a mid-point connection whichconstitutes the other terminal of the direct-current traction-motorcircuit, means for providingan intentional grounding-circuit at someselected part of the direct-current tractionmotor circuit, aground-detection relay for detecting faultcurrents due to an accidentalground at some other place, said ground-detection relay having anoperating coil and a holding coil, and also having an element forincapacitating the ignition-circuit means of the rectifying devices whenthe ground-detection relay is in its responsive condition, means forenergizing said operating coil to be refir sponsive to currents in saidintentional grounding-circuit, means for energizing said holding coilwith a steady current which is approximately at the holding-in value,during the normal fault-free operation of the traction-motor means, andmeans for increasing this holding-coil current to a holding-in valuewhen said ground-detection relay is energized.

References Cited in the file of this patent UNITED STATES PATENTS2,059,064 Tritle et al Oct. 27, 1936 2,106,844 Harder et al Feb. 1, 19382,576,518 Knauth Nov. 27, 1951

